Billings, Montana (CNN) -- Surveying his land that lies in the shadow of the Rocky Mountains, farmer Mike Scott states the obvious.
"We are in the middle of Montana," he said. "You don't expect to have an oil spill."
But an oil spill is exactly what Scott and hundreds of other Montana residents who live on the Yellowstone River are grappling with after an Exxon Mobil pipeline fouled the waters a week ago with about 42,000 gallons of crude oil.
It's just a short walk from Scott's house to the water. And the oil.
Sticky brown puddles of the crude oil rest on the water's surface. Absorbent boom set up by Exxon workers catches some of the oil. Plenty of oil though continues to flow downstream towards Scott's neighbors. Thick patches of oil discolor the fields on the river's edge. That's what worries the farmer most.
"I don't know what oil will do to the microorganisms that actually grow stuff," Scott said. "I am also worried that the remediation efforts will take forever, take 50-to-60 percent of this place out of production for an indefinite future."
Scott's wife Alexis Bonogofsky stays away from the river, near the pen where they now keep their 100 goats that usually would roam their property.
After days of wading into the oily waters to document the damage to their farm, now, Alexis said, the smell of the oil causes her to have headaches and nausea.
She said she doesn't believe Exxon's assurances that the oil does not pose health risks.
"They told us to move our livestock away from it, told us to stay away from it," Alexis said. "But they told us at the same time it doesn't have any harmful effects on human health or livestock health."
How the pipeline ruptured at a section that runs under the river remains a mystery. Exxon officials said the pipeline was buried five to eight feet under the riverbed and surrounded by cement.
The pipeline failed as the river was flooding the area with a deluge of water caused by melting snow and heavy rains. While it's not clear if the flooding contributed to the break in the pipeline, the high waters carried the oil far beyond the river's banks.
The flooding along the river concerned Exxon even before the breach. The company shut down the line for a day in May 2010 to run a risk assessment, said Exxon Mobil Pipeline Co. president Gary Pruessing.
"After that work was done, we still thought we had a safe line so we restarted it," Pruessing said, "We have learned something new here.
"Obviously, there is something that we did not consider, something we will learn about once the investigation is done."
Pruessing said the company now believes the pipeline leaked oil into the river for 49 minutes. Initially Exxon officials said the leak lasted about 30 minutes. Pruessing said that the estimate of how much oil actually leaked remains between 750 to 1,000 barrels or 32,000 to 42,000 gallons of oil.
Exxon has 350 workers slowly mopping up the globs of oil that have spread across some 20 miles of the river, Pruessing said.
"I can assure you that we are here to do the full clean up and will be here as long as necessary until the job is done," he said.
But for Bonogofsky, the spill has already changed the land where she has spent most of her life.
"You go down to where the oil is," she said, "And you don't hear anything any more. No birds, no toads, no crickets, nothing. It's just silent."